US20060106394A1 - Off-axis anchor guidance system - Google Patents

Abstract

Disclosed is a guided bone anchoring device comprising a head, a shank and a passage for receiving a guide wire, the passage having a longitudinal center axis which is not concentric to the longitudinal center axis of the shank. Also disclosed is a system for guiding bone anchors, the system comprising: a guide wire, an anchor comprised of a shank wherein the shank has an offset bore at the distal end which is adapted to allow the guide wire to slide through the bore, a dilator having a longitudinal slot wherein the longitudinal slot allows the guide wire to extend through the longitudinal slot when the anchor is positioned within the dilator, and a driving device which is adapted to engage the proximal end of the anchor.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application is a continuation-in-part of patent application Ser. No. ______, entitled “An Implant Assembly And Method For Use In An Internal Structure Stabilization System” filed on Nov. 16, 2004, the disclosure of which is hereby incorporated by reference.
TECHNICAL FIELD
• This application relates generally to the field of medical implant devices and more particularly to systems and methods for inserting and guiding bone anchoring devices.
BACKGROUND INFORMATION
• Orthopedic injuries, deformities, and degenerative diseases often require intervention in the form of surgery for placing implants to stabilize an internal structure, promote healing, and relieve pain. In the area of spinal surgery, for example, a common procedure includes placement of pedicle screws that are joined by a connecting rod spanning between these screws. Once placed, the rod must be firmly secured to the bone securing elements to provide a stable construct which effectively immobilizes or creates a controlled dynamic motion to a corresponding portion of the spine.
• One problem when connecting the rods to the pedicle screws is to position the rods in place as quickly as possible without doing more damage to the surrounding tissue and muscle of the patient. In order to reduce this damage, procedures have been developed that allow the physician to secure the pedicle screws in the bony portion of the spine and to then connect the rods or brace between the pedicle screws. Techniques have been developed to allow the surgeon to perform this procedure in a minimally invasive manner, utilizing a percutaneous method, inserting screws through small ports and avoiding an open approach.
• In one such procedure, a surgeon identifies the desired vertebral level and pedicle positions via standard techniques. Once the target vertebrae are identified, a small incision is made through the patient's skin and a tracking needle (or other device) is inserted to pinpoint exactly where each pedicle screw is to be placed. A fluoroscope, or other x-ray technique, is used to properly position the tracking needle. Once the proper position is located, a guide wire is positioned with its distal end into the pedicle of vertebrae. The surgeon then slides a series of continuing larger sized dilators down the guide wire. The surgeon may also slide a hole tapping instrument over the guide wires. The hole tapping instrument may be used to tap a hole in the pedicle. After the hole is tapped, a cannulated pedicle screw and a modified screw driver may be inserted down the guide wire until the screw reaches the desired position. The position may be again checked with fluoroscopic techniques. For purposes of this application, a cannulated pedicle screw is defined as a pedicle screw that contains a cannulation centered and running entirely through its longitudinal axis.
• After the position of the cannulated pedicle screw has been confirmed, the surgeon is ready to screw the cannulated pedicle screw into the vertebrae. After the cannulated pedicle screw has been inserted, this procedure may be repeated for each additional level. When one or more pedicle screws are in place, a brace or rod may be positioned by techniques known in the art. Under current practice, the physician then must work the brace, or other supporting device, so that each brace end is positioned properly with respect to the preplaced pedicle screws, and tighten the brace to each pedicle screw to complete assembly.
• Once a patient recovers and become active, the brace may be subject to relatively large structural forces. These forces are applied to the shanks of the cannulated pedicle screws. Consequently, it is the shanks of the cannulated pedicle screws that resist the applied forces. To be more specific, it is the portion of the screw shank that is positioned within the pedicle of the vertebral body (approximately two-thirds of the length of the screw from the distal tip of the screw towards the proximal end of the screw) (the highest stress region is that region of the pedicle screw that is nearest the entry point of the pedicle, which tends to be about two thirds up from the distal tip of the pedicle screw).
• When conventional pedicle screws are cannulated, a significant portion of their cross-sectional area is removed to create the cannulation. The cannulation, therefore, causes higher stress in the remaining portions of the shank which is subject to the applied forces. This causes a significant weakening of the screw. This weakening can cause failure of the pedicle screw which means that the patient would have to undergo additional surgery to have the pedicle screws replaced.
• In order to minimize the reduction in strength of the screws, the cannulations are made as small as possible. This means that the guides wires must also be small, which may lead to advancement, kinking, breakage, or other problems during surgery. Inadvertent advancement of the guide wire is a critical concern to clinicians. If the guide wire becomes bent through off-angle manipulation by the surgeon, as the tap or screw is inserted, the tap or screw pushes the guide wire forward. This unwanted guide wire advancement could cause the guide wire to push forward through the anterior wall of the vertebral body, causing trauma to the patient.
• What is needed, therefore, is a device and system which will allow for anchors to be guided and inserted into patients while maintaining the structural integrity and safety of the anchor and/or the guide wire.
SUMMARY
• In response to these and other problems, in one embodiment, there is a guided bone anchoring device comprising: a head, a shank having a proximal end and a distal end, wherein the proximal end is coupled to the head, and an off-axis bore for accepting a guide.
• Thus various aspects of this disclosure allows the shanks of wire guided anchors to resist larger forces than conventional cannulated screws because the offset bores do not cause a cannulation through the entire length of the anchor. Furthermore, the offset bore may be of a relatively larger diameter when compared to the conventional cannulation of conventional cannulated pedicle screws. The larger diameter bore results in a larger diameter guide wire which: increases the strength of the guide wire; reduces kinking; allows a surgeon to have tactile feedback regarding the placement and location of the guide wire; and allows the surgeon to maintain hold of the proximal end of the guide wire at all times throughout the procedure. Furthermore, the relative short length of the offset bore reduces the friction between the instruments and the guide wire, thereby reducing the likelihood of guide wire advancement.
• These and other features and advantages will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. It is important to note the drawings are not intended to represent the only aspect of the invention.
• Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the invention is intended to encompass within its scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1. illustrates an isometric view of an example medical implant device which incorporates one or more aspects of the present invention.
• FIG. 2 illustrates a cross-section view of an illustrative embodiment of an anchoring device which incorporates one or more aspects of the present invention.
• FIG. 3aillustrates a front view of an illustrative embodiment of an anchoring device which incorporates one or more aspects of the present invention.
• FIG. 3billustrates a front view of an alternative embodiment of an anchoring device which incorporates one or more aspects of the present invention.
• FIG. 3cillustrates a front view of yet another alternative embodiment of an anchoring device which incorporates one or more aspects of the present invention.
• FIG. 4 illustrates a driving device coupled to an anchor which incorporates one or more aspects of the present invention.
• FIG. 5 illustrates an isometric view of an illustrative embodiment of a dilator which incorporates one or more aspects of the present invention.
• FIG. 6 illustrates one step in an illustrative embodiment of a procedure for implanting a guided anchoring device.
• FIG. 7 illustrates one step in an illustrative embodiment of a procedure for implanting a guided anchoring device.
• FIG. 8 illustrates one step in an illustrative embodiment of a procedure for implanting a guided anchoring device.
• FIG. 9 illustrates one step in an illustrative embodiment of a procedure for implanting a guided anchoring device.
• FIG. 10 illustrates one step in an illustrative embodiment of a procedure for implanting a guided anchoring device.
• FIG. 11 illustrates one step in an illustrative embodiment of a procedure for implanting a guided anchoring device.
• FIG. 12 illustrates an example stabilization device configuration which may result from the procedure described in reference to FIGS.6 to11.
DETAILED DESCRIPTION
• Turning now toFIG. 1, there is presented one illustrative embodiment of an anchoring system showing certain aspects of the present invention. As shown, amedical implant device10 includes ananchor12 which may be coupled to arod receiving part14. In some embodiments, therod receiving part14 may includenoncontiguous walls16 and18 which form a channel20 for receiving arod22. In some embodiments, there is aclosure member24 which engages thewalls16 and18 and thus applies pressure to therod22 to effectively clamp about therod22, thereby positionally securing therod22 relative to theanchor12. Such a closure member is more fully described in a co-pending and commonly assigned U.S. patent application Ser. No. 10/805,967 filed on Mar. 22, 2004 entitled “CLOSURE MEMBER FOR A MEDICAL IMPLANT DEVICE” (hereafter “the '967 patent application), which is hereby incorporated by reference.
• In the illustrated embodiment, theanchor12 has ashank26 having aproximal end28 and adistal end30. In this example embodiment, theanchor12 illustrates a screw and thus has ahelical thread32 positioned about theshank26. It is important to note that although a screw is illustrated, theanchor12 could be any suitable anchor having any suitable surface. For example, theanchor12 could be a ring shank fastener, a barb, a nail, a brad or a trocar. Furthermore, theanchor12 may also have an expandable diameter which allows the anchor to “lock” into the bone after placement.
• Proximal to thedistal end30, there may be abore34 the center of which may be rotatedly offset from alongitudinal axis36 of theshank26. As illustrated, thebore34 extends from thedistal end30 to the side of theshank32.
• FIG. 2 illustrates a cross sectional view of one aspect of theanchor12. In this view, it can be seen that theanchor12 has ahead38 coupled to theproximal end28 of theshank26. In this embodiment, thebore34 begins at thedistal end30 and exits through aside40 of theshank26. In other words, in relation to thelongitudinal axis36 of theshank26, thebore34 is angularly rotated about thedistal end30 of the shank forming an acute angle a with the longitudinal axis. For the purposes of this application, the term “off-axis” shall be taken to mean a bore having a center longitudinal axis which is non-concentric in relation to the center longitudinal axis of the shank. Thus, an off-axis bore may run either laterally parallel to the longitudinal axis of the shank or be angularly rotated about the distal end of a shank as illustrated inFIG. 2.
• As previously described, anchors, such asanchor12, are typically subjected to relatively large forces. The large external forces and the overall placement of such anchors result in localized regions of higher stresses which may cause the anchor to break in such regions. A typical region of higher stress is illustrated asregion42. Theregion42 is generally located along theshank26 below theproximal end28 of theshank26. Note that in this embodiment, the cross sectional area of theshank26 inregion42 has not been reduced. Thus, the full cross-sectional area of theshank26 is available in this region to resist the applied forces. Furthermore, the use of the full cross-sectional area (without cannulation) reduces the stress in theregion42 which may greatly increase the strength of theanchor12.
• This arrangement is in contrast to conventional cannulated pedicle screws which have a cannluation extending entirely through the screw along their longitudinal center axes. The cannulation causes a reduction in cross sectional area at high stress locations which contributes to a failure of the cannulated screw.
• Thebore34 may receive a guide wire (not shown). Because the bore does not cause a cannulation through the entire length of the anchor, the bore may be of a relatively larger diameter when compared to conventional cannulated pedicle screws. The larger diameter bore allows the guide wire to also have a larger diameter, which increases the strength of the guide wire and reduces wire advancement and kinking. Furthermore, the larger diameter increases the strength of the guide wire and may allow a surgeon to have tactile feedback regarding the placement and location of the guide wire.
• By having the guide wire exit the side of the anchor, the surgeon can keep hold of the proximal end of the guide wire at all times throughout the procedure. This may help ensure that the guide wire does not advance as the screw is slid down the wire. Additionally, the relative short length of the bore34 (compared to a conventional cannulated screw) will tend to reduce the friction between the instruments and the guide wire, thereby reducing guide wire advancement. Guide wire advancement will also be reduced because the guide wire is pulled out prior to advancing the anchor so there is no guide wire advancement during screw insertion as with conventional cannulated systems.
• Turning now toFIG. 3a, there is illustrated a front view of one embodiment of theanchor12. As illustrated, the bore34 (FIG. 2) forms a generally elongated opening46 with the front side of theshank26. In some embodiments, there may be a series ofsmaller openings46a formed by the threads and the bore. In this illustrative embodiment, thehead38 of theanchor12 may include an externalhelical thread50. In some embodiments, thehelical thread50 may be a “reverse” screw thread which may be adapted to engage a corresponding reverse screw thread of the rod receiving part14 (FIG. 1). For purposes of this application, a reverse screw thread is a thread designed to engage a corresponding thread in an opposite rotational direction when compared to conventional threads. Thehead38 may include various recesses and/orprotrusions52 to engage a driving device (not shown) that may be used to drive theanchor12 into the bone (not shown). In some embodiments, the driving device may also be used to remove an installed anchor from a bone.
• FIG. 3billustrates a front view of an off-axis pedicle screw56 incorporating various aspects of the present invention. As illustrated, abore57 forms a generally elongated opening55 with one side of ashank59. The off-axis pedicle screw56 has an alternative embodiment of ahead58. In this illustrative embodiment, thehead58 may include one or more splines, for example splines60a,60b, and60c. Thesplines60a,60b, and60cmay be equally spaced circumferentially around thehead58. In some head embodiments, thesplines60a,60b, and60cmay be spaced at unequal distances circumferentially around thehead58. Thesplines60a, and60b, and60cmay include surface protrusions, recesses and/or texturing to enhance coupling of the off-axis pedicle screw56 with a ring of a bone fastener assembly (not shown). In some embodiments, sides of thesplines60a,60b, and60cmay have a tapering so that the splines form a dovetail connection with a ring. In some embodiments, the spline width may be tapered so that a good interference connection is established when the bone screw is coupled to a ring.Splines60a,60band60cmay include one or more projections (not shown) to facilitate coupling thehead58 to an inner surface of a ring which may be part of the rod receiving part assembly.
• Turning now toFIG. 3c, there is illustrated a front view of another alternative embodiment of an off-axis pedicle screw62. In some embodiments, the off-axis pedicle screw62 may be a have ahead64 which is adapted to be a fixed angle fastener as depicted inFIG. 3c. Such fixed angle fastener heads are well known in the art.
• FIG. 4 illustrates theanchor12 coupled to aguide wire72. As will be explained in detail below, once theguide wire72 is in place, theguide wire72 may be slipped through the bore34 (not shown) of theanchor12 as illustrated inFIG. 4. The anchor may also be coupled to adriving device70.
• As illustrated inFIG. 4, a distal end of drivingdevice70 is positioned in anexternal sleeve74. In some embodiments, thesleeve74 may be coupled to the rod receiving part14 (FIG. 1) of themedical implant device10. The drivingdevice70 may include anouter shaft76, aninner shaft78, andremovable handle80. Theouter shaft76 may include atextured portion82. In some embodiments, thetextured portion82 may facilitate rotation of theouter shaft76 without the use of theremovable handle80.
• In some embodiments, the distal end of inner shaft78 (not shown) may be coupled to theanchor12 during use. Theproximal end81 of theinner shaft78 may be coupled to theremovable handle80. Thus, during the anchor placement, theinner shaft78 may be rotatable relative toouter shaft76 so thatanchor12 can be inserted into a bone. In some embodiments, a proximal portion of theinner shaft78 may include a coupling portion (not shown) which is adapted to mate with theremovable handle80. Theremovable handle80 may also be adapted to fit other instruments which may be used in the procedure such as a bone awl and/or a bone tap (not shown).
• FIG. 5 illustrates an isometric view of an illustrative embodiment of adilator84 which may be used with various aspects of the present invention. As will be explained below, dilators are typically used in spinal procedures. Thedilator84 has alongitudinal slot86 which allows theguide wire72 to extend outside of the dilator during use.
• Referring now to FIGS.6 to11, the manner of using certain aspects of the present invention will now be described. The surgeon identifies the desired vertebral levels and pedicle positions via standard techniques. Once the target vertebrae are identified, a small incision is made through the skin and a tracking needle (or other device) is inserted to pinpoint exactly where each anchor is to be placed. A fluoroscope, or other x-ray technique, may be used to properly position the tracking needle. Once the proper position is located, theguide wire72 may be positioned with its distal end against the pedicle, in this case pedicle86 of vertebrae L4 as illustrated inFIG. 6.
• As shown inFIG. 7, the surgeon may then slide a series of continuing largersized dilators88a,88b,88c, and88ddown theguide wire72. Approximately four or five dilators are used until a diameter suitable for passing the anchor and its extensions is achieved. In some embodiments, the last dilator used will be the slottedside dilator84 discussed with reference toFIG. 5. Once slotteddilator84 is in place, theother dilators88athrough88dmay be removed. In some embodiments, a bone awl and/or bone tap may inserted over the guide wire to tap a hole into the pedicle in preparation for receiving theanchor12, which in this case may be a pedicle screw. This tap will usually be a size slightly smaller than the pedicle screw thread size selected for that patient and that level.
• After the hole is tapped and the inner dilators, such as dilators88a-88dare removed, the surgeon is ready to introduce theanchor12 into the vertebrae. As shown inFIG. 8, prior to inserting the anchor12 (e.g., pedicle screw), theguide wire72 is placed through the off-axis bore34 (not shown) of theanchor12. Theanchor12 may be coupled to the drivingdevice70 as previously described. The drivingdevice70 engages the proximal end of theanchor12. As theanchor12 and the distal end of the drivingdevice70 enters the slotteddilator84, theslot86 of the dilator allows theguide wire72 to extend beyond the passage of thedilator84 as illustrated inFIG. 9.
• Once theanchor12 is in position, which may be verified by flourscopy techniques, theguide wire72 may be removed. It may also be desirable at this stage to also remove thedilator84. To accomplish this, theremovable handle80 may be removed in order to allow thedilator84 to slip over the drivingdevice70 as shown inFIG. 10. Once theanchor12 is in position, the drivingdevice70 may then be rotated into a proper position, as shown inFIG. 11. The surgeon may then screw theanchor12 into the pre-tapped hole in vertebrae L4. Pressure on the drivingdevice70 forces the anchor to be in-line with theexternal sleeve74. A similar procedure may be repeated for each additional level, in this case level L5.
• Once the pedicle screws are in place, an assembly may be coupled to the pedicle screws. For instance,FIG. 12 shows an examplemedical implant device100. A similarmedical implant device100 is described further in co-pending and commonly assigned U.S. patent application Ser. No. 10/690,211 filed Oct. 21, 2003 titled “SYSTEM AND METHOD FOR STABILIZATION OF INTERNAL STRUCTURES” (hereafter “the '211 patent application), the disclosure of which is hereby incorporated herein by reference. More specifically,medical implant device100 may be a stabilization device that may include pedicle screws (or “anchors”)102aand102bthat are inserted into vertebrae of a patient's spine, such as vertebrae L4 and L5, respectively. The pedicle screws have off-axis bores103aand103bwhich have been used in conjunction with guide wires (not shown) to guide the screws to the proper location.Assemblies104aand104bmay be coupled topedicle screws102band102a, respectively.Such assemblies104aand104beach form a receiving member for receiving closure member (e.g., setscrew106aor106b). Generally, such receiving member formed byassemblies104aand104bis a noncontiguous (e.g., open-back member) having at least two walls, such aswalls108aand110a, that are separated by slots.
• In this illustrative embodiment,closure member106aandwalls108aand110aare formed to have complementary threads that are formed in a manner that aids in preventing splaying of the receiving members. In the specific implementation shown, closure member106 andwalls108aand110aof the receiving member are dovetail configurations, such as described in the '967 patent application. Of course, other interlocking configurations, may be used in alternative implementations. As further shown inFIG. 12, a brace (or “rod”)112 extends fromassembly104atoassembly104b, and closure members (e.g., set screws)106 are used for securing afirst end114 of thebrace112 to thepedicle screw102aand theother end116 of thebrace112 topedicle screw102b.
• Thus, themedical implant device100 may be installed using various aspects of the present invention. As previously described, theanchors102aand102bare able to resist larger forces than conventional cannulated screws. Furthermore, because thebores103aand103bdo not cause a cannulation through the entire length of the anchors, the bores may be of a relatively larger diameter when compared to conventional cannulated pedicle screws. The larger diameter bore allows the guide wire to also have a larger diameter, which increases the strength of the guide wire, reduces kinking, allows a surgeon to have tactile feedback regarding the placement and location of the guide wire, and allows the surgeon can keep hold of the proximal end of the guide wire at all times throughout the procedure. The relative short length of the bore reduces the friction between the instruments and the guide wire, thereby reducing guide wire advancement.
• It is important to note that any such advantages and benefits described in this application may not apply to all embodiments of the invention. When the word “means” is recited in a claim element, Applicant intends for the claim element to fall under 35USC 112, paragraph 6. Often a label of one or more words precedes the word “means”. The word or words preceding the word “means” is a label intended to ease referencing of claims elements and is not intended to convey a structural limitation. Such means-plus-function claims are intended to cover not only the structures described herein for performing the function and their structural equivalents, but also equivalent structures. For example, although a nail and a screw have different structures, they are equivalent structures since they both perform the function of fastening. Claims that do not use the word means are not intended to fall under 35USC 112, paragraph 6.
• The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims. For instance, various embodiments of the present invention could be integrated into various navigational systems, such as the GE EM Tracking system.
• The abstract of the disclosure is provided for the sole reason of complying with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Claims (20)

1. A system for guiding bone anchors, the system comprising:

a guide wire;

an anchor comprising of a shank having a proximal end and a distal end, wherein the shank has an offset bore at the distal end which is adapted to allow the guide wire to slide through the bore;

a dilator having a longitudinal slot wherein the longitudinal slot allows the guide wire to extend through the longitudinal slot when the anchor is positioned within the dilator; and

a driving device which is adapted to engage the proximal end of the anchor.

2. The system ofclaim 1 wherein the bore extends through the distal end of the shank to a point located along a side of the shank.

3. The system ofclaim 1 wherein the bore is not concentric to a longitudinal center axis of the shank.

4. The system ofclaim 1 wherein the driving device further comprises:

an outer shaft,

an inner shaft rotatedly disposed within the outer shaft having an distal end and proximal end, and

a removable handle coupled to the proximal end.

5. The system ofclaim 4 wherein the outer shaft is adapted to couple with a rod receiving portion of a medical implant device and the distal end of the inner shaft is adapted to engage the anchor.

6. A method for positioning a bone anchor into a bone, the method comprising: making an incision in the skin to allow access to the bone;

positioning a distal end of a guide wire to a desired location within the bone to slideably receive the dilators, and bone anchor;

sliding a dialator having a longitudinal slot over the guide wire;

sliding the guide wire into a bore at the distal end of the anchor and causing the guide wire to exit the bore at a side surface opening.;

positioning the anchor into the dialator such that the guide wire extends through the longitudinal slot; and

positioning the anchoring device at the desired location as defined by the distal end of the guide wire.

7. The method ofclaim 6 further comprising sliding a series of continuing large dialator over the guide wire to increase the visual area of a surgical site.

8. The method ofclaim 6 further comprising preparing a bore to receive the anchoring device.

9. The method ofclaim 8 further comprising rotating the anchoring device to drive the anchoring device into the bone.

10. The method ofclaim 9 further comprising checking the position of the guide wire with fluoroscopic techniques.

11. A guided bone anchoring device comprising:

a head;

a shank having a proximal end and a distal end, wherein the proximal end is coupled to the head; and

a bore extending through the distal end of the shank to a point located along a side of the shank.

12. The bone anchoring device ofclaim 11 wherein the head is bulbous.

13. The bone anchoring device ofclaim 12 wherein the head has an exterior helical thread adapted to mate with a rod receiving device.

14. The bone anchoring device ofclaim 13 wherein the thread is a reverse thread.

15. The bone anchoring device ofclaim 11 wherein the shank has an exterior helical thread adapted to mate with the bone.

16. The bone anchoring device ofclaim 12 wherein the head has at least one longitudinal spline configured to couple with a ring within a rod receiving part of an implant system.

17. The bone anchoring device ofclaim 12 wherein the head is generally U-shaped.

18. A guided bone anchoring device comprising:

a head;

a shank having a proximal end, a distal end, and a longitudinal center axis running between the proximal and distal end; and

a passage for receiving a guide wire, the passage having a longitudinal center axis which is not concentric to the longitudinal center axis of the shank.

19. The bone anchoring device ofclaim 18 wherein the head is bulbous and has an exterior helical thread adapted to mate with a rod receiving device.

20. The bone anchoring device ofclaim 19 wherein the thread is a reverse thread.

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